As many of you know, analyst's estimate that Windows Server Active Directory (AD) is deployed by over 90% enterprises in the world. It is the world's most widely used corporate directory and in the 15 years since AD was first introduced, many organizations have developed and deployed hundreds and thousands of applications that rely on LDAP and other AD APIs such as System.DirectoryServices.

Additionally, Active Directory's Domain join and Group Policy capabilities are some of the most widely used enterprise technologies on the planet. For most organizations they are the standard for managing the access and configuration policies for Windows servers and Windows clients.

So it's no surprise that now that these organizations are looking for ways to use the cloud to improve their economics and deliver new competitive advantage, they are looking for ways to virtualize these applications and servers and move them into IaaS cloud services like Azure.

Unfortunately, these legacy applications, many of which were developed by employees and contractors who no longer work at the company, don't support modern authentication protocols like OAuth2.0 or SAML. So rewriting them to use modern authorization protocols is prohibitively expensive.

To work around this challenge, customers generally take two approaches:

Set up a VPN/Expressroute to support a direct connection between these apps and servers deployed in their IaaS cloud service provider of choice and the on-premises corporate AD.

Run domain controller VMs in their IaaS cloud service and have those domain controllers synchronize to their on-premises Active Directory servers using a VPN/Expressroute connection.

The approaches present serious challenges in terms of reliability, ease of administration and cost. In the first approach, transient network glitches frequently impact application availability. In the second approach, the costs can be substantial. Administrators need to manage DCs running in VMs – including patching, monitoring, troubleshooting replication, performing backups, ensuring high-availability and SLAs etc.

We built Azure AD Domain Services because we saw firsthand the struggles customers were having here and we were pretty sure we could provide a simple, reliable, cost effective solution.

Introducing Azure AD Domain Services

Azure AD Domain Services provides managed cloud based domain services such as domain join, group policy, LDAP & Kerberos/NTLM authentication in the Azure cloud that are fully compatible with Windows Server Active Directory. With these services, you get the full value of Windows Server AD in the cloud domain, without having to deploy, manage, monitor and patch domain controllers.

And because Azure AD Domain Services is part of your existing Azure AD tenant, users login using the same corporate credentials they use for Azure AD, and you can use existing groups and user accounts to secure access to resources.